Revert "perf(rpc): search the block log for a record instead of scanning it"

This reverts 539d8da. The change duplicates #87, which was opened two days
earlier and makes the same argument: `record_for_hash` has the height from the
block tree, the log is ordered by height, so the lookup is a search.

#87 also covers `Context::block_hash_at_height`, which 539d8da missed.

What 539d8da had and #87 does not - a benchmark, the sweep-against-a-scan
equivalence tests, `block_by_height_without_an_applied_tip_reads_the_log`, and
five further mutations - moves to #87 rather than being dropped.

This branch keeps only the chain-info fold, which nothing else covers.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rabbitson87

crates/node/src/block_source.rs

@@ -14,7 +14,7 @@ use bitcoin::hex::FromHex as _;
 use bitcoin_rs_chain::{BlockTree, NodeId, TipSnapshot};
 use bitcoin_rs_index::BlockSource;
 use bitcoin_rs_primitives::Hash256;
-use bitcoin_rs_rpc::{BlockBodySource, BlockLog};
+use bitcoin_rs_rpc::{BlockBodySource, BlockLog, BlockRecord};
 use parking_lot::RwLock;
 
 /// Reads decoded Bitcoin blocks from the shared in-memory log.
@@ -82,7 +82,7 @@ impl BlockSource for NodeBlockSource {
             tree.read().active_node_at_height(height)?.hash
         } else {
             let guard = self.blocks.read();
-            guard.record_at_height(height)?.hash
+            record_at_height(&guard, height)?.hash
         };
         self.resolve_block_by_hash(height, active_hash)
     }
@@ -98,7 +98,7 @@ impl BlockSource for NodeBlockSource {
             tree.read().active_node_at_height(height)?.hash
         } else {
             let guard = self.blocks.read();
-            guard.record_at_height(height)?.hash
+            record_at_height(&guard, height)?.hash
         };
         source.block_body_range(height, hash, offset, len)
     }
@@ -138,7 +138,7 @@ impl NodeBlockSource {
     fn cached_body_bytes(&self, height: u32, hash: Hash256) -> Option<Vec<u8>> {
         let block_hex = {
             let guard = self.blocks.read();
-            let record = guard.record_at_height_hash(height, hash)?;
+            let record = record_at_height_hash(&guard, height, hash)?;
             (!record.block_hex.is_empty()).then(|| record.block_hex.clone())
         }?;
         Vec::<u8>::from_hex(&block_hex).ok()
@@ -298,6 +298,47 @@ fn serialized_header(
     })
 }
 
+fn record_at_height(records: &[BlockRecord], height: u32) -> Option<&BlockRecord> {
+    if let Ok(index) = usize::try_from(height)
+        && let Some(record) = records.get(index)
+        && record.height == height
+        && index
+            .checked_sub(1)
+            .and_then(|previous| records.get(previous))
+            .is_none_or(|previous| previous.height < height)
+    {
+        return Some(record);
+    }
+
+    let mut index = records
+        .binary_search_by_key(&height, |record| record.height)
+        .ok()?;
+    while index > 0 && records[index.saturating_sub(1)].height == height {
+        index = index.saturating_sub(1);
+    }
+    records.get(index)
+}
+
+fn record_at_height_hash(
+    records: &[BlockRecord],
+    height: u32,
+    hash: Hash256,
+) -> Option<&BlockRecord> {
+    let mut index = records
+        .binary_search_by_key(&height, |record| record.height)
+        .ok()?;
+    while index > 0 && records[index.saturating_sub(1)].height == height {
+        index = index.saturating_sub(1);
+    }
+    while index < records.len() && records[index].height == height {
+        if records[index].hash == hash {
+            return Some(&records[index]);
+        }
+        index += 1;
+    }
+    None
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -306,7 +347,6 @@ mod tests {
     use bitcoin::consensus::encode::serialize;
     use bitcoin_rs_chain::NodeStatus;
     use bitcoin_rs_primitives::Hash256;
-    use bitcoin_rs_rpc::BlockRecord;
     use std::error::Error;
 
     type TestResult = Result<(), Box<dyn Error>>;

crates/rpc/Cargo.toml

@@ -52,7 +52,3 @@ criterion.workspace = true
 [[bench]]
 name = "chaininfo"
 harness = false
-
-[[bench]]
-name = "blocklookup"
-harness = false